The present invention relates to a thermal transfer recording material. More particularly, the present invention relates to a thermal transfer recording material for use in forming printed images having excellent heat resistance, solvent resistance, scratch resistance, and like properties.
Conventional common thermal transfer recording materials include one wherein a heat-meltable ink containing a wax as the main component of the vehicle thereof is applied on a foundation, and another wherein a heat-meltable ink containing a resin as the main component of the vehicle thereof, for the purpose of forming printed images of high quality even on a paper sheet having poor surface smoothness or forming printed images having good fastness.
Recently, bar code printers or label printers using a thermal transfer recording material have been used for printing bar codes or like codes which are used for management of parts or products in the production process of manufacturing factories, merchandise management in the distribution field, management of articles in the use field, and the like.
Among such articles to be given bar codes, there are those exposed to high temperatures after provision of bar codes. For example, a heat treatment at about 180.degree. C. is conducted in production processes for printed wiring boards and a heat treatment at about 250.degree. C. in inspection processes for semiconductors.
Bar codes or like codes used for product management in manufacturing factories or the like require good solvent resistance because they frequently come into contact with solvents, oils and the like, and bar codes or like codes used in the distribution field or the like require good scratch resistance because they are frequently subjected to rubbing.
Further, besides printing bar codes, thermal transfer printers have been used for the production of many products which are produced in small quantities, including outdoor advertising, election posters, general posters, standing signboards, stickers, catalogs, pamphlets, calendars, and the like in commercial printing field; bags for light packaging, labels for containers for foods, drinks, medicines, paints, and the like, and binding tapes in packaging field; labels for indicating quality characteristics, labels for process control, labels for product management, and the like in apparel field. These articles also require scratch resistance, solvent resistance or heat resistance.
However, there are no conventional thermal transfer recording materials which have excellent transferability and can form printed images meeting such heat resistance, solvent resistance and scratch resistance at the same time.
That is, although the above-mentioned conventional thermal transfer recording material with a heat-meltable ink layer whose vehicle is composed of a wax as a main component is good in transferability, the printed images obtained therefrom are sometimes collapsed when exposed to a high temperature of about 250.degree. C. to become illegible, and are also poor in solvent resistance and scratch resistance. The above-mentioned conventional thermal transfer recording material with a heat-meltable ink layer whose vehicle is composed of a resin, such as ethylene-vinyl acetate copolymer, as a main component forms printed images which are comparatively good in heat resistance, solvent resistance and scratch resistance, but its transferability is inferior to that of the recording medium having the wax-predominant ink layer because of the high melt viscosity of its ink layer.
Further, a thermal transfer recording material using a heat-meltable ink containing bisphenol A diglycidyl ether as a vehicle is proposed (Japanese Examined Patent Publication No. 60-59159). However, this bisphenol A type epoxy resin has a disadvantage that a pigment such as carbon black is not favorably dispersed thereinto. For this reason, the recording material is poor in transferability, resulting in unclear printed images. With respect to recording materials for use in thermal transfer recording system, poor transferability is a fatal drawback.
An object of the present invention is to provide a thermal transfer recording material which has excellent transferability and can form printed images which have such heat resistance that they stand high temperatures up to about 280.degree. C., and further have excellent solvent resistance and scratch resistance.
This and other objects of the present invention will become apparent from the description hereinafter.